1. Field of the Invention
The present invention relates to cooling systems for internal combustion aircraft engines. More particularly, the present invention relates to a parallel flow coolant circuit for internal combustion aircraft engines having horizontally opposing piston cylinders.
II. Description of the Relevant Art
In an aircraft engine, as in all engines which experience energy loss in the form of heat, cooling is required to control such heat. This cooling is provided typically in the form of a liquid or a gas. When in gas form, bypassing air functions primarily as the coolant.
Beginning with the first flight of the Wright Brothers in 1903, liquid cooled piston engines have been used in aviation. The engine which powered that historic flight was a liquid cooled four cylinder, 200 cubic unit engine. Since those early days of flying the principle of employing a fluid to cool an aircraft engine has gone essentially unchanged.
Air cooled engines began to flourish in the 1930's in the form of the air cooled radial engine. The United States depended almost entirely upon the air cooled radial engine to power its military aircraft in World War II.
After 1945, both military and commercial aircraft began to shift reliance from piston driven engines to jet engines. On the other hand, the civilian light plane market grew in the postwar years, and the air cooled horizontally opposed piston engine expanded rapidly to become the mainstay of what has become known today as general aviation.
Yet in all its development, conventional horizontally opposed piston engines still rely largely upon air cooling. This is not because air cooling is more efficient than liquid cooling; just the opposite is true. However, because of certain disadvantages of liquid cooling, air cooling has been the method of choice.
One disadvantage of liquid cooling is the lack of reliability of the coolant plumbing system. However, modern technology including new materials and a better understanding of stress and thermal expansion has largely overcome this disadvantage.
Another important disadvantage of liquid cooling is the uneven cooling of the cylinders and pistons by the liquid coolant. This uneven cooling results in temperature variation from one cylinder and its component parts to the next. Such variations commonly lead to equipment failure.
The main cause of this uneven cooling is the construction of the cooling manifold which advances coolant from one cylinder to the next in a series, thereby resulting in undesirable temperature variation from one cylinder to the next. According to this known system, an extremely wide temperature difference exists between the first cylinder to be cooled and the last.